1. Field of the Invention
The present invention relates to a multi-channel low power communication method and apparatus.
2. Description of the Related Art
As smart devices are popularized, users of the mobile internet are continuously increasing. With an increase in real time traffic such as high capacity multimedia, for example sound, image, and the like, a bandwidth and speed of a network device for accepting the traffic are also increasing. With rapid spread of high performance intelligent mobile terminals, demands of the users are continuously diversified and increased.
However, energy consumption is increasing in proportion to a performance increase of the network device. Since wireless communication devices equipped with a high communication technology use a strong processor, an affluent memory, a wide screen, and an open operation system (OS), an energy budget of a wireless communication interface with a limited battery capacity should be extremely limited. Wireless communication systems are rapidly developing to accept additional elements and technologies to add new functions and increase the performance. However, development in a battery size and a battery capacity is relatively slow. Accordingly, in regard to the wireless communication systems, there is a desire for a method for using the limited battery capacity longer and more efficiently.
Due to a limited power capacity of a wireless communication mobile terminal, a research for reducing the energy consumption is actively conducted. In particular, it is known that, in mobile devices such as a smart phone, a tablet, a notebook, and a sensor, most of energy is inefficiently consumed in the wireless communication interface.
Since the battery capacity is limited in the mobile terminal or the sensor, a technology for minimizing energy consumption is necessary. In a mobile node, most of energy is consumed in a central processor unit (CPU) and the wireless communication interface. The CPU may reduce energy consumption by variably controlling a clock frequency and a voltage supply according to a load to be processed and requirements of an application program. That is, the CPU may be operated at a low frequency and a low voltage if possible, or the operation may be suspended until the task is generated when a task to be processed is absent.
A wireless interface may reduce power consumption by two methods as follows.
1) The wireless interface is awake only when there is data to be exchanged with another wireless device. Otherwise, a power save mode is maintained to reduce energy consumption.
2) When a received packet does not correspond to an identifier (ID) of the wireless interface, data processing is not performed to reduce energy consumption.
3) According to the above technologies 1) and 2), the efficiency may be deteriorated since an environment and condition provided to the mobile node are not taken into consideration. Therefore, the conventional wireless modem physical layer has reduced energy consumption by setting an operation frequency to be low, by minimizing a voltage supply or decreasing complexity, and by variably controlling the clock frequency and the voltage supply according to a load to be processed.
However, reduction in the operation frequency, the voltage supply, and the complexity is limited with a conventional semiconductor processing technology. Since those three factors are in trade-off relationships with the performance, meeting of performance requirements of the system is limited.
Unsatisfactory energy efficiency, interference, coverage, transmission capacity, unstable transmission rate, and the like are typical limits of a wireless local area network (WLAN) technology. According to a spread of smart devices equipped with a WLAN chip, a great number of access points (AP) are being used. However, an actual increase in performance is not meeting expectation due to signal collision caused by overlap of a service area between APs and a hidden node problem.
In particular, since the WLAN is required to perform high speed digital processing to support a high performance service, a high frequency clock is used and a great hardware size is required. In addition, since a relatively high voltage is used, power consumption is extremely high.
A power saving protocol of a medium access control (MAC) level introduced to overcome the high power consumption defines a sleep mode. When there is no packet to be exchanged, the WLAN is converted into the sleep mode to interrupt an unnecessary clock or voltage supply of the circuit, thereby reducing the power consumption. In a MAC layer, the energy consumption may be reduced by a method that keeps an awake state only when there is data to be exchanged with another wireless device using a separate control signal periodically exchanged and maintains a power save mode when there is no data to be exchanged.
Here, the control signal may have a relatively long time period due to interrupt processing of MAC layer hardware and software. Due to the trade off relationships between the performance, for example a service quality including throughput and delay, and the power consumption, use of the power save mode of the MAC layer is limited.
Furthermore, in an active mode, not the sleep mode, a reception standby mode needs to be maintained since a packet receiving time is unknown. Even when a packet is received, whether the received packet is to be received by a corresponding terminal and whether recovery of the packet will succeed are not guaranteed. Therefore, reduction in the power consumption is limited with the conventional technology.